Subsea vehicle assisted pipeline commissioning method

ABSTRACT

The present invention is directed to a method for completing the commissioning of a subsea pipeline by purging with a compressed gas to dewater and dry the line wherein the operation is done on the seabed. More specifically, the method is carried out with a subsea vechicle (hereinafter “SV”) that powers pumps located on the seabed or are carried by the SV to inject/remove chemical, dewater, and dry, the pipeline. The present invention may be part of the commissioning of a new or old pipeline or a new portion of a pipeline in which a purging of the line with a compressed gas and drying of the line is required. After commissioning, product flows through the pipeline.

RELATED APPLICATION

This application is a divisional application of Ser. No. 09/892,314,filed Jun. 26, 2001, entitled “Subsea Vehicle Assisted PipelineCommissioning Method”, now U.S. 6,539,778, based on provisionalapplication 60/275,215, filed Mar, 13, 2001, entitled “Subsea to SubseaRemotely Operated Vehicle Assisted Pipeline Commissioning Method”.

FIELD OF THE INVENTION

The present invention is directed to commissioning methods for subseapipelines. More specifically, the present invention is directed to acommissioning method wherein the operation is carried out on the seabedrather than at the surface.

BACKGROUND OF THE INVENTION

U.S. Pat. No. 5,883,303 discloses and describes an apparatus and methodfor pigging, flooding and pressure testing pipelines.

The above patent is directed to the testing required when a new pipelineis placed in operation. However, when commissioning a subsea pipeline,or adding a new segment to an existing offshore pipeline, it is oftendesired to follow the hydrostatic pressure testing with an inert gas orspecified medium to purge/dewater the subsea pipeline, and/or injectspecified chemicals, to dry the inside of the line before flow of theoil/gas in the pipeline.

The dewatering of a subsea pipeline by the prior art has been at surfacelevel, usually on a surface vessel, boat, structure or platform. Thisrequires that long lines of coiled tubing, hose, or pipe, be used. Theprior art method uses large distances of coiled tubing, hose, or pipe,to connect the pipeline to a pump mobilized on the deck of a supportvessel to remove the water and dry the line before product is allowed topass through the line. Also required by the prior art method are largepumps, compressors, compressor boosters and surface support vesseland/or vessels, to support the large volume of compressed gases andfluids pumped through the significant distances to fill the new portionof the pipeline with the gas and fluids.

The method of the present invention eliminates the larger volume ofcompressed gas and fluids, the higher pressure of the compressed gas andfluids, the large pumps/compressors, compressor boosters, long distancesof coiled tubing/hose/pipe, and substantial surface supportvessel/vessels, all required by the prior art methods.

SUMMARY OF THE INVENTION

The present invention is directed to a method for completing thecommissioning of a subsea pipeline by purging with a compressed gas todewater and dry the line wherein the operation is done on the seabed.More specifically, the method is carried out with a subsea vechicle(hereinafter “SV”) that powers pumps located on the seabed or that arecarried by the SV to inject/remove chemical, dewater, and dry, thepipeline. The present invention may be part of the commissioning of anew or old pipeline or a new portion of a pipeline in which a purging ofthe line with a compressed gas and drying of the line is required. Aftercommissioning, product flows through the pipeline.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a surface support vessel positioned toserve a subsea pig launcher/receiver on a manifold on the seabed and asubsea pig launcher/receiver on a second manifold connected by a portionof a subsea pipeline;

FIG. 2 is a schematic view of a subsea pig launcher/receiver stabbedinto a manifold on the seabed and a SV carrying a fill and test packageof equipment to carry out a commissioning method;

FIG. 3 is a view of one possible panel face connected to the subsea piglauncher/receiver and a representative schematic of the valves includedin the panel for carrying out a commissioning method;

FIG. 4 is a schematic view of a subsea pig launcher/receiver stabbedinto a manifold on the seabed and assisted by a SV;

FIG. 5 is a view of one possible panel face connected to the subsea piglauncher/receiver and a representative schematic of the valves includedin the panel for carrying out a commissioning method;

FIG. 6 is a representative schematic view of the pump of the fill andtest package of equipment connected at one subsea pig launcher/receiverpushing the pig through the pipeline to the subsea pig launcher/receiverat the other end of the pipeline;

FIG. 7 is a schematic of the SV tethered from the support vessel andpowering the pump to push the pig through the subsea pipeline to asubsea pig launcher/receiver;

FIG. 8 is a representative schematic of the subsea pig launcher/receiverwhere the pig has arrived in the receiver;

FIG. 9 is a representative schematic of the SV attaching the pressurepump to asubsea pig launcher/receiver to perform a high-pressurehydrostatic test on the pipeline;

FIG. 10 is a schematic of the SV disconnecting the pressure pump to thesubsea pig launcher/receiver after completeing the high-pressurehydostatic commissioning test and opening a valve to release thepressure in the pipeline;

FIG. 11 is a representative schematic of the SV attaching a compressedgas source to one subsea pig launcher/receiver to force the pig throughthe pipeline from the launcher to the subsea pig receiver;

FIG. 12 is a schematic of the SV attaching the dewatering pump andremoving the water from the pipeline to move the pig through thepipeline from one pig launcher/receiver to the second subsea piglauncher/receiver;

FIG. 13 is a schematic of the SV tethered from the support vessel andpowering the pump at one subsea pig launcher/receiver to reduce thepressure on the launcher side of the pig which enables the compressedgas to push the pig toward the receiver;

FIG. 14 is a schematic of the SV at one subsea pig launcher/receiver todisconnect the compressed gas source after filling the pipeline withgas; and

FIG. 15 is a schematic of the completed dewatered pipeline and therecovery of the SV and other equipment as required, to the supportvessel.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE PRESENT INVENTION

Offshore drilling for oil/gas is continuing to expand at furtherdistances from shore and at greater depths. Subsea pipelines areutilized to transport the discovered product to a variety of dispositionpoints. These points include existing or new offshore trees, manifolds,pipelines, platforms, or onshore facilities. As new wells are completedsubsea pipelines flowing the product are tied through manifolds toexisting pipelines that are already in place to bring the product toshore. As dictated by law, the new sections of pipeline requirehydrotesting to make certain that the line has no leaks and in somecases, contains no water. In addition to hydrotesting, other steps inthe commissioning of the pipeline may be required, including dewatering,drying, cleaning, and installing chemicals. The present inventionrelates to any or all the steps as related to the commissioning of thesesubsea pipelines carried out on the seabed rather than at the surface.

Once a well is completed, a pipeline is connected to the well for movingthe product to shore. The pipeline is often not extended all the way toshore but is tied through a manifold or connection to offshorefacilities. Manifolds as used herein may have a variety of specificstructures; however, the common function for the purpose herein is thatsections of pipelines are connected to other facilities, including otherpipelines via various connection assemblies referred to herein asmanifolds. Also common to a manifold as used herein is that there isstructure to provide internal access to the pipeline. The subseaperformance or operation of the commissioning method, the presentinvention, will be described as a method of commissioning a pipelinebetween two manifolds; however, it is understood that the commissioningis not limited to that portion of a pipeline between two manifolds butincludes any subsea pipeline or pipeline segment, most particularly onewhich has or could have both ends at the seafloor at the time of testingand commissioning

The present invention is directed to a commissioning method wherein theoperation is carried out on the seabed rather than at the surface. It isillustrated by using a subsea vehicle to assist in the operation andassumes that valves require to be mechanically operated from the subseavehicle. This is only one embodiment of the invention since the degreeof assistance necessary by the subsea vehicle may be materially reducedwith the use of automated valves not requiring mechanical operation. Thesubsea vehicle need not carry the pumps are other equipment as shown inthe embodiment illustrated by the drawings.

Referring to FIG. 1, a surface support vessel (or multiple vessels ifrequired) 10 is positioned at the surface between two manifolds 12 and14. A subsea pipeline 16 is connected to the manifolds 12 and 14. Thevessel 10 supports the commissioning (the internal cleaning of thepipeline, the hydrostatic testing for leaks and the removal of water andthe partial product fill) of pipeline 16 before product is allowed totransported by pipeline 16 for passage to shore. The commissioningprocess is assisted by a subsea vehicle (SV) 18. The SV may be aremotely operated vehicle (ROV) or autonomous underwater vehicle (AUV)as these vehicles are known in the prior art, or they may be modifiedfor the purposes of the present invention, or may include any manned orunmanned vehicle that has a system that can manipulate the hoses, pumpsand other equipment used in the commissioning method. The SV 18 may betethered to the support vessel 10 and may have a tether managementsystem (TMS) assuring that the tether is not in the way of anyoperation. The SV 18 provides the electrical system for it's operationand other equipment, as will be described hereinafter. Alternatively, anelectrical umbilical cord may be part of the tether and tether system.The SV 18 installs, by use of it's robotic arm 19, a subsea piglauncher/receiver 20 on manifold 12 (it being understood that thedirection of operation is not material and the launcher/receiver may beplaced on manifold 14). In an equally desirable embodiment, the piglauncher/receiver may be installed on the pipe end and laid with thepipe at the time the pipeline is laid. The pig launcher/receiver 20 isshown as stabbed into the top of manifold 12; however, piglauncher/receiver 20 may be in any orientation. The SV 18 then installsa subsea pig launcher/receiver 30 on manifold 14. Similarly, thisassembly may also be installed on the pipe end before the pipe is laid,and then laid with the pipeline. Pig launcher/receiver 20 is installedwith a pig 22, which is a known structure used in cleaning ormaintaining fluids separate in a pipeline, in the launcher/receiver 20(see FIG. 2). Pig launcher/receiver 20 and pig receiver 30 can each havea panel 24 and 34, respectively, that is operated by the robotic arm 19(see FIG. 2) on the SV 18. Pig launcher/receiver 20 and receiver 30 mayalready be installed or may have been installed as part of the pipelineinstallation.

The SV 18 returns to the support vessel, (if required), 10 aftercompleting the installation of the pig launcher/receiver 20 and the pigreceiver 30 to acquire a fill and test package 40 which includes anumber of pumps and lines that are connected to either panel 24 or 34 aswill be described in more detail hereinafter. The package 40 ispreferably held by the SV 18 during the remainder of the commissioningprocess; however, landing the package 40 on the sea floor near piglauncher/receiver 20 is also an alternative. The fill and test package40 may alternatively be more than one package mounted on differentskids.

Referring now to FIG. 2, manifold 12 is at one end of pipeline 16 andmay have one or more other pipelines connected at manifold 12. Thesubsea pig launcher/receiver 20 is connected to the manifold in anyorientation that allows access to pipeline 16. A pig 22 is in the piglauncher/receiver 20. A panel 24 (see FIG. 3) on pig launcher/receiver20 contains passageways, valves and gauges to control the flow of fluidsand gasses through pipeline 16. The robotic arm 19 on the SV 18, orother suitable control provision, begins the flow of water behind pig 22by opening free flooding valve 51 to force the pig 22 through pipeline16 to clean any solid debris that remains in the pipeline after beinglaid in place. Upon opening valve 51 in panel 24, seawater entersthrough opening 52 of a filter 54, where the seawater is filtered andchemical may be injected, and passes through panel 24 and out opening 55before pushing pig 22 through pipeline 16 until the pressure on eitherside of the pig equalizes. A check valve (not shown) on the pig receiver30 allows the air in front of the pig to exit the receiver side of thepipeline 16. The SV 18 then moves to the pig receiver 30.

Referring now to FIG. 4, manifold 14 may have a vertical section towhich the subsea pig receiver 30 is connected so as to have access topipeline 16. A panel 34 (see FIG. 5) on pig receiver 30 containspassageways, valves and gauges to control the flow of fluids throughpipeline 16. The SV 18 opens the discharge valve 61 of panel 34. It isrecognized that the method described assumes that each panel 24 and 34requires the assistance of the SV 18 to open and close the valves;however, if the valves on either panel are automated and are operatedfrom the surface or the SV 18, then the SV need not make trips from thepig launcher/receiver 20 to the pig receiver 30 as described. The SV 18then moves to the pig launcher/receiver 20. It is recognized that thespecific sequence of events will depend upon the requirements ofspecific applications, and that the sequence stated here isrepresentative but is not the only method in which the described systemmay be operated.

Referring to FIG. 6, the SV 18 then closes free flowing valve 51 on thepanel 24. A line 42 from the fill and test package 40, specifically froma high volume pump, is connected to port 56 on the panel 24 and valve 57is opened. Seawater is pumped through line 42 and the panel 24 and outopening 55 to force pig 22 toward the pig receiver 30.

The operation of filling the pipeline 16 with seawater pumped from piglauncher/receiver 20 to pig receiver 30 is illustrated in FIG. 7. Anaspect of the present invention is that the pumping is done from thefill and testing package 40 held by SV 18, or placed on the seabed,rather than pumps mobilized on board the surface support vessel 10 Thus,the entire operation is done subsea rather than using the long lines andlarge equipment that is necessary if done on the surface. The umbilicalfor the SV 18 may be thousands of feet long and the subsea operation ofthe present invention eliminates those number of feet of coiled tubingusually used in this operation. Pumping is continued until the pig 22arrives in the pig receiver 30. Arrival of the pig at the receiver isdetected by any of a variety of pig detectors commonly known in theindustry, and an indication of arrival can be sensed from pressurechanges or transients at the launcher/receiver. The SV 18 then moves tothe pig receiver 30.

Referring now to FIG. 8, the SV 18 positioned at the pig receiver 30closes valve 61 on panel 34 in preparation for the hydrostatic testingof pipeline 16. The SV 18 then moves to the pig launcher/receiver 20.

Referring now to FIG. 9, SV 18 uses robotic arm 19 to stab line 42 fromthe fill and test package 40, specifically from a high pressure pump,into the hot stab 56 on the panel 24 and valves 57 and 60 are opened. Itis recognized that, depending on the specific application, it may bepreferred to perform these steps in a different sequence, and it may bepreferred to connect the pump to either the launcher/receiver orreceiver end of the pipeline for hydrostatic testing. Seawater is pumpedthrough line 42 to increase the pressure in the pipeline 16 to testinglevel. The pressure is monitored by pressure gauge 58 and data recorder63. The test pressure is maintained for a length of time to make certainthat there are no leaks in the pipeline 16. Any drop in pressureindicates a problem and the first measure may be to repressure to testpressure and wait another length of time to make certain the pipeline 16will maintain pressure.

Upon successful completion of the hydrostatic testing of the pipeline16, the SV 18 disconnects line 42, referring now to FIG. 10, and closesvalve 57 and 60 and vents the pipeline through a flow restrictor and/orfree flooding valve 51 on the panel to depressure the pipeline 16. Theflow of the water in the pipeline 16 will exit through valve 51;however, the flow is controlled and measured by flow meter 59 so thatthe de-pressurization is slow and even and does not cause any vibrationsor other disturbances to the pipeline 16. Monitoring of the pressuregauge 58 and flow meter 59 as the flow of water is through opening 55and valve 51 is maintained until the internal pressure reaches ambientpressure, meaning that the pressure inside and outside the pipeline 16are the same. The SV 18 then moves to the pig receiver 30.

Referring now to FIG. 11, a compressed gas pack (gas source that may benitrogen or air) 70, is connected to the pig receiver 30. The gas packmay be mounted to manifold 14, laid on the subsea floor, or connected bya hose/tubing line from a remote site or from the surface previously orat this time in the operation. The connection may be made by anysuitable method, including using the robotic arm 19 of the SV 18 to stabthe line 72 from the pack 70 into the hot stab 66 in panel 34 andcompressed gas inlet valve 67 is opened to force in the compressed gasbehind the pig 22. The SV 18 then moves to the pig launcher/receiver 20.

Referring now to FIG. 12, SV 18 uses robotic arm 19 or other suitablemethod to connect line 42 from the fill and test package 40,specifically from the dewatering or vacuum pump, into port 56 of thepanel 24. The valve 57 is opened and the pipeline 16 is dewatered.Seawater is pumped through opening 55, valve 57 and line 42, reducingthe pipeline internal pressure at the launcher/receiver end so that amodest volume of compressed gas can push pig 22 by differential pressuretoward the pig launcher/receiver 20.

The operation of dewatering and pigging the pipeline 16 by pumping waterthrough the pig launcher/receiver 20 from pipeline 16 is illustrated inFIG. 13. An aspect of the present invention is that the pumping is donefrom the fill and test package 40 held by SV 18 rather than pumpsmounted on the support vessel 10. The operation being done subseaeliminates the long lengths of coiled tubing, hoses, or piping, and thelarge pumps that are necessary when the operation is done at thesurface. The volume of compressed gas is significantly reduced. Sincethe gas in the pipeline is at a relatively low pressure, significantlysmaller quantity of compressed gas is required as compared to prior art.An additional advantage is that a smaller support vessel may beutilized. The operation of dewatering and pigging, meaning that thewater is forced out of pipeline 16 by the pig 22 being pushed bycompressed gas, until equilibrium is reached then the pig is drawn tothe launcher/receiver by the dewatering pump until the pig 22 arrives atthe pig launcher/receiver 20 at which time there is no further water tobe sucked out of the pipeline 16. The SV 18 then shuts off thedewatering pump and closes valve 47 on the panel 24. The pipeline 16 isnow ready for product to be passed through the pipeline 16. The productwill not be contaminated by water and the nitrogen or other compressedgas does not materially affect the product. The SV 18 disengages line 42and makes any necessary securing of manifold 12 as is deemed necessaryor desirable. The SV 18 then moves to the pig launcher/receiver 30.

Referring now to FIG. 14, the SV 18 closes valve 67 and disengagescompressed gas line 72 from panel 34. The compressed gas pack 70 is madesecure or connected to the SV 18 to be returned to surface. The SV 18makes any necessary securing of manifold 14 as is deemed necessary ordesirable. The commissioning operation that includes cleaning,hydrostatic testing and dewatering is complete. It is understood thatall steps are not necessary if the operation includes less than thecommissioning operation as set forth. Additionally, an additional stepmay be included whereby the product is introduced into the pipeline.

Referring now to FIG. 15, the SV 18 carrying the fill and test package40 is recovered to the support vessel 10.

The commissioning operation has been described in detail, but it isunderstood that this detail is representative, and that variations inthe method may be appropriate for specific applications. Significantimprovements to the prior art have been set forth. Modifications andadditions may be added without changing the commissioning operation asset forth. For example the commissioning method is carried out on apipeline with both ends on the seafloor or one end on the seafloor andthe operation is carried out at that end before the pipeline isconnected to manifolds or other structure. Another example, the panel 24may have a valve 67 that when open provides access to vacuum gauge 69.The robotic arm 19 and pumps on the fill and test package 40 are poweredby electric or hydraulic power. The tether connecting the support vessel10 includes a substantial electrical source that powers the pumps on thefill and test package 40 directly or powers a hydraulic power sourcewhich then drives the pumps. There may be three separate pumps on thefill and test package 40 or two pumps, the low volume high pressure pumpbeing able to operate both to add water to the pipeline 16 or as adewatering pump to suck water from the pipeline 16, or just one pump.There are many changes in details that may be made such that watertreating may be added, filters may be added, more than one pig may beused, methanol or other chemicals may be added between pigs, the pig mayinclude tracking means to name some; however, changes in detail do notchange the method as set forth and described.

1. A method of dewatering a pipeline between first and second subseamanifolds, comprising: providing a test and fill package operated by asubmersible vehicle (SV), the test and fill package having at least onesubsea pump dimensioned to remove a volume of water disposed between thefirst and second subsea manifolds; attaching the subsea pump to thefirst subsea manifold on the pipeline; delivering a compressed gassource to the second subsea manifold on the pipeline using the SV, thesecond subsea manifold having a subsea pig launcher/receiver with a pigtherein; activating the subsea pump to reduce internal pressure in thepipeline; and introducing compressed gas from the compressed gas sourceto move the pig by differential pressure toward the first subseamanifold, thereby dewatering the pipeline.
 2. The method according toclaim 1 wherein the SV is tethered to a support vessel on the surface.3. The method of claim 1, wherein the compressed gas source consists ofone or more subsea compressed gas packs.
 4. The method of according toclaim 1 wherein a pump mounted on the test and fill package pumps waterinto the pipeline to a level sufficient for hydrostatic pressure testingprior to dewatering the pipeline.
 5. The method of claim 4, wherein asingle pump on the test and fill package performs both hydrostaticpressure testing and dewatering.
 6. The method of claim 4, whereinseparate pumps on the test and fill package perform hydrostatic pressuretesting and dewatering.
 7. A method of dewatering a pipeline between afirst and second subsea manifolds comprising: connecting a subseacompressed gas pack via a compressed gas inlet valve to a first subseamanifold having a subsea pig launcher/receiver with a pig therein;opening the gas inlet value to force the compressed gas behind the pig;connecting a pump operated by a submersible vehicle (SV) to the secondsubsea manifold; activating the pump to draw water, the pig and gasdelivered from the compressed gas pack through the pipeline, the gaspack having sufficient compressed gas to move the pig from one of thesubsea manifolds to the second subsea manifold in conjunction withreduced internal pipeline pressure provided by the pump; wherein theaction of the pump and the compressed gas provide for dewatering thepipeline without need for a surface pump or a surface supply ofcompressed gas.
 8. A method according to claim 7 wherein the SV has arobotic arm for connecting and disconnecting the pump to the pipeline.9. The method according to claim 7 wherein the SV is tethered to asupport vessel on the surface.